Prior art forming machines include a pair of forming dies mounted for movement between an end-to-end relationship and an overlapping relationship such that forming faces thereof engage a workpiece supported between the dies in order to provide forming of the workpiece. Usually the elongated dies are in the form of rectilinear die racks which are slidably mounted on upper and lower machine bases that define a work space forward of a rear connecting portion extending between the bases. See for example, U.S. Pat. Nos. 2,995,964 and 3,793,866, the latter one of which is assigned to the assignee of the present invention. However, it is also possible to have the elongated dies mounted on rotary spindles such that partially circular forming faces thereof form a workpiece mounted between the spindles in the manner disclosed by U.S. Pat. No. 4,045,988 which is also assigned to the assignee of the present invention.
In the prior art machines of the above described type, the dies are separately driven by a pair of drive motors whose driving action is coordinated by one or more gears in order to insure an equal extent of movement of each die. Hydraulic piston and cylinder units function as the drive motors for the machine of the U.S. Pat. No. 2,995,964 and the driving movement of forming die racks upon piston rod retraction and extension is coordinated by a gear that is meshed with a pair of coordinating racks in order to insure an equal extent of movement of each forming die rack. Rotary hydraulic motors are utilized in the machine of the U.S. Pat. No. 3,793,866 in order to drive the forming die racks and are interconnected by a gear train that insures an equal extent of movement of each forming die rack. Likewise, the elongated dies of the rotary forming machine of the U.S. Pat. No. 4,045,988 are also driven by a pair of hydraulic motors whose driving operation is interconnected by a gear train. With such types of machines, a small amount of backlash that may be present with the coordinating gearing can permit one of the dies or die racks to continue to move a very small distance on the order of one or several thousandths of an inch, after the other die or die rack has already stopped moving.
Solid workpieces are usually formed by the type of machine described above to include gear teeth or splines and, once forming has been performed over the complete circumference of the workpiece, the formed teeth or splines also help to coordinate the movement of the forming dies or racks. Formed teeth or splines on solid workpieces usually have the requisite strength to provide the coordination between the driving movement of the associated pair of dies or die racks due to the solid nature of the teeth or splines.
U.S. Pat. Nos. 3,982,415 and 4,028,922, both of which are assigned to the assignee of the present invention, disclose forming machines and dies thereof that are capable of forming splines or teeth in a thin-walled annular sleeve of a workpiece. This type of forming is particularly useful for forming power transmission members such as splined clutch hubs used for vehicle automatic transmissions. Forming begins by mounting of the workpiece with its sleeve positioned over a toothed mandrel located between the dies which are positioned in an end-to-end relationship. Movement of the dies from the end-to-end relationship into an overlapping relationship meshes the die and mandrel teeth with the sleeve of the workpiece located therebetween so as to provide forming of the splines or teeth on the sleeve. It has been found that forming of such thin-walled sleeves requires an accurate control of the extent of die movement in order to provide sleeves whose formed splines or teeth are of a precise shape without any out of roundness. In this connection, reference should be made to the U.S. Pat. No. 4,028,922 which discloses a die tooth pattern and forming process for preventing out of roundness on the formed sleeve. Also, it is very important that the dies move in a precisely coordinate manner whose extent of movement is accurately controlled so that the forming terminates immediately after all of the splines or teeth have been formed in order to prevent deformation of the formed teeth or splines by continued movement of one or both dies.